[RFC/PATCHSET 0/5] perf ftrace: Implement function latency histogram (v1)

[Namhyung Kim]

Hello,

I've implemented 'latency' subcommand in the perf ftrace command to
show a histogram of function latency.

To handle new subcommands, the existing functionality is moved to
'trace' subcommand while preserving backward compatibility of not
having a subcommand at all (defaults to 'trace').

The latency subcommand accepts a target (kernel, for now) function
with -T option and shows a histogram like below:

  $ sudo ./perf ftrace latency -a -T mutex_lock sleep 1
  #   DURATION     |      COUNT | GRAPH                                          |
       0 - 1    us |       2686 | ######################                         |
       1 - 2    us |        976 | ########                                       |
       2 - 4    us |        879 | #######                                        |
       4 - 8    us |        481 | ####                                           |
       8 - 16   us |        445 | ###                                            |
      16 - 32   us |          1 |                                                |
      32 - 64   us |          0 |                                                |
      64 - 128  us |          0 |                                                |
     128 - 256  us |          0 |                                                |
     256 - 512  us |          0 |                                                |
     512 - 1024 us |          0 |                                                |
       1 - 2    ms |          0 |                                                |
       2 - 4    ms |          0 |                                                |
       4 - 8    ms |          0 |                                                |
       8 - 16   ms |          0 |                                                |
      16 - 32   ms |          0 |                                                |
      32 - 64   ms |          0 |                                                |
      64 - 128  ms |          0 |                                                |
     128 - 256  ms |          0 |                                                |
     256 - 512  ms |          0 |                                                |
     512 - 1024 ms |          0 |                                                |
       1 - ...   s |          0 |                                                |
  
It basically use the function graph tracer to extract the duration of
the function.  But with -b/--use-bpf option, it can use BPF to save
the histogram in the kernel.  For the same function, it gets:

  $ sudo ./perf ftrace latency -a -b -T mutex_lock sleep 1
  #   DURATION     |      COUNT | GRAPH                                          |
       0 - 1    us |       4682 | #############################################  |
       1 - 2    us |         11 |                                                |
       2 - 4    us |          0 |                                                |
       4 - 8    us |          0 |                                                |
       8 - 16   us |          7 |                                                |
      16 - 32   us |          6 |                                                |
      32 - 64   us |          0 |                                                |
      64 - 128  us |          0 |                                                |
     128 - 256  us |          0 |                                                |
     256 - 512  us |          0 |                                                |
     512 - 1024 us |          0 |                                                |
       1 - 2    ms |          0 |                                                |
       2 - 4    ms |          0 |                                                |
       4 - 8    ms |          0 |                                                |
       8 - 16   ms |          0 |                                                |
      16 - 32   ms |          0 |                                                |
      32 - 64   ms |          0 |                                                |
      64 - 128  ms |          0 |                                                |
     128 - 256  ms |          0 |                                                |
     256 - 512  ms |          0 |                                                |
     512 - 1024 ms |          0 |                                                |
       1 - ...   s |          0 |                                                |


You can get the patches at 'perf/ftrace-latency-v1' branch on

  https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git


Thanks,
Namhyung


Namhyung Kim (5):
  perf ftrace: Add 'trace' subcommand
  perf ftrace: Move out common code from __cmd_ftrace
  perf ftrace: Add 'latency' subcommand
  perf ftrace: Add -b/--use-bpf option for latency subcommand
  perf ftrace: Implement cpu and task filters in BPF

 tools/perf/Makefile.perf                    |   2 +-
 tools/perf/builtin-ftrace.c                 | 443 +++++++++++++++++---
 tools/perf/util/Build                       |   1 +
 tools/perf/util/bpf_ftrace.c                | 154 +++++++
 tools/perf/util/bpf_skel/func_latency.bpf.c | 113 +++++
 tools/perf/util/ftrace.h                    |  81 ++++
 6 files changed, 724 insertions(+), 70 deletions(-)
 create mode 100644 tools/perf/util/bpf_ftrace.c
 create mode 100644 tools/perf/util/bpf_skel/func_latency.bpf.c
 create mode 100644 tools/perf/util/ftrace.h


base-commit: 8ab774587903771821b59471cc723bba6d893942
-- 
2.34.0.rc2.393.gf8c9666880-goog